BSA Improved Model

[jirushi]

Hi, I recently bought a prewar BSA.
From reading John Milewski's great book "The Book of the BSA Air Rifle 1905 to 1939", I think it is an Improved Model (A).
The serial number cannot be read entirely anymore; this gun must have seen some life / had rust. But it seems to start with 126. See photos.

It looked quite tired. I lightened the stock a bit with fine steel wool and alcohol (being extra careful with the chequiering), and it is now getting a few layers of CCL oil.
I have made the metal a bit blacker by degreasing with acetone and then using Ballistol Schnellbrünierung. Some parts hardly had any finish left, so I thought this way the gun would have more protection for the future.

However, the internals need more attention than the exterior.
Power is relatively low (about 6.6 ft/lbs using .177 7,0 gr RWS). And it doesn't feel/sound right. Not a twang, but more a "boing".
The leather seal doesn't look great. At one spot, it is clearly damaged.
The piston has three phosphor bronze rings. I believe these should help sealing, or perhaps they are meant to reduce friction of the piston in the cylinder?
I think they do neither of those.
I tested their sealing capacity by removing the leather seal, and moving the cylinder up and down the compression chamber with my finger pressed no the transfer port.
Air clearly leaked past the rings.
Furthermore, they seem to make the cylinder move less freely through the cylinder.
Not sure why they are there; probably a tinkering project of a previous owner?

Then the springs. Twin springs, but one of them isn't flat section. It has a loose fit over the spring guide, or in the cylinder. Not ideal.
Together, they are about 21 cm (8,3") long. It is (too?) easy to put the trigger block back on the cylinder. I would expect more preload.

Hopefully the tap is ok. I will test it when I have a good piston seal.
Something that I noticed is that my .177 pellets don't fall to the end of the hole in the tap. In my .177 Light Pattern, they fall deeper.
I have tried RWS Meisterkugeln and a few types of JSB.

A few things on the "to do list":
- find or make a replacement leather piston seal. The usual parts shops don't sell this early flat type. It is about 5,5 mm thick. I might have to find a thick piece of leather and a 1.1" round cutter. Or try a 1.1" cup type seal (although I think this will reduce the swept volume quite a bit).
- find a flat section spring, or a pair of them.
- decide what to do with the phosphor bronze piston rings.

Any advice/input is welcome.

Many thanks, Louis



This stock length works well for me


Piston rings and damaged leather seal

[Garvin]

Louis if the bronze rings aren't doing anything positive, couldn't you just remove them altogether and be no worse off than normal?

[draitzer]

To me it looks like your piston seal is the typical shallow cup shape with a filler washer.

I've not seen any reference to metal piston rings on these. Also your piston 'head end' may be longer than normal, as the slot usually intrudes into the 'head' portion. Possibly a custom tuner's creation?

My records show original twin springs were about 10" total overall length, with 21 coils each.

Some info on pistons, spring swaps, etc. is available on Danny's Gallery at:
https://forum.vintageairgunsgallery....l-tips-faqs-2/

Good luck!
Don R.

[Lakey]

Wow, another interesting BSA comes to the surface. Thanks for sharing photos.

I have heard of occasional BSA/Lincolns with Phosphor Bronze piston rings before, and Dennis Hiller depicts a drawing of just such a piston on page 19 of his " Collectors Guide to Air Rifles - enlarged fourth edition " so maybe it was a prototype/experimental thing that was dropped for mainline production. That piston was on a gun with a serial number 49209, and it was a .22 .
The piston does seem professionally made, and the finish is good, so it could have been the work of a professional gunsmith. Also it does seem an extreme mode for a home enthusiast to do.

If your compression cylinder is in good condition, and true in dimensions you would have thought that either the three rings, or the conventional leather piston washer would have been an adequate seal, but to have both seems excessive to me. The piston rings rely on a spring action to hold them to the cylinder walls, so that in itself would generate more friction for the mainspring to fight against. They also rely on proper lubrication to function, so a thicker oil than normal is needed I think.

The pellets not falling to the bottom of the tap is due to the fact that the 'Improved Model' was the first BSA to feature a tapered Tap. The earliest production guns had parallel taps, which in practice were difficult to load. The pellets needed a seating pin. The Improved models tapered tap was an improvement, allowing pellets to be loaded without a seating pin, however the taper wasnt as wide as later models.

In my experience, BSA seem to function smoother with spring pairs rather than a full length spring, however that pairs need to be quite soft. If the steel is too strong, the firing cycle of the gun is harsh. Last time I looked both Protek and Knibbs were doing the paired springs.

Thanks for sharing details of your interesting gun.

Lakey

[Benelli B76]

If the piston is of normal length I would think that the extended piston head needed to accommodate all those rings would be too long and would reduce power by reducing swept volume of air.

Baz

[trajectory]

That's a very interesting find.

Your photo is very good & shows the three split ring washers very well. Below the washers there are, on my screen at any rate, what looks to me to be two further brass coloured rings. Are they really thin rings or grooves around the piston that have picked up a coloured reflection or something like that. I'd be interested to know what they are please.
Looks a great find & I am sure will be of interest to fans of older BSA air rifles. Just makes you wonder how many others there might be that nobody realises they have...

If you have a UV light I wonder if that might help reveal the full serial number?

[jirushi]

Thank you for the input so far, gentlemen. Much appreciated.

@ Don R., thank you for the info on the springs. That is very useful. Also the link from Garvin's forum is fantastic, with the technical info/tips.
The leather seal is a flat disk, about 5.5 mm thick. I will pick up a 1.1" leather cup type piston seal today, which will probably seal better, but reduce the swept volume. We'll see.
I might have to find a thick piece of leather, and a metal pipe with 1.1" inner diameter, to make a new flat type seal.

@Lakey, thank you for your very interesting comments.
The piston also has a "star" stamped on it, near the skirt. I think it is original BSA, but the rings might indeed have been a gunsmith's work?
And is it best to push the pellets deeper into the tap, or is it fine to just drop them in and let the air pressure do the rest?
Unfortunately, I don't think that Knibbs or Protek sell the paired springs anymore. (Knibbs: "BSA Round Section Wire Mainsprings (Pair) Part No. STD20 ***No longer available" - Protek: only non flat section springs on their website).

@Baz, the overall length of the piston (rod not included) is about 114 mm (4.49").
The "height" of the head is about 18.5 mm (0.73"). Would be interesting to know if it is a standard size, or longer to accomodate the rings.









When in the cylinder, the bronze rings still have "gaps". Perhaps not the best fit?


The "star" is on many parts of the gun. I believe this was the case with these guns anyway? Not sure what it means (must have a look in the BSA book!).
The "0" is also under the barrel. Does this mean that the tap is original to the gun?